Such spherical joint endoprostheses have been known for a long time and have proven themselves in surgical procedures. Unfortunately there are a number of problems associated with the known endoprostheses. For example, during implantation of a femur shaft component of a total hip joint endoprosthesis after the insertion of the shaft into the modular area of the femur bone, it is difficult to achieve the exact orientation of the shaft piece in such a manner that the artificial joint ball to be connected with the femur shaft component shows no luxation tendencies after the implant. This is caused by the shaft piece and the conical pin being arranged at a fixed angle to each other for the assembly of the conical interference fit connection between the shaft piece and the spherical head.
An adjustment to the individual needs of the patient is very difficult, since even with the most modern x-ray technology, these needs are usually first recognized during surgery, and the surgeon cannot simply try various endoprostheses until the right one is determined from a supply. An adjustment to the individual patient's needs includes the already mentioned reduction of the luxation tendency, occasionally a lengthening of the leg, a force equalization of the muscular antagonists in all four directions (medially, laterally, dorsally, ventrally), or the compensation for a valgus or varus formation of the thigh neck of the leg in question.
Examples of prior art devices which attempt to solve the above difficulties with varying degrees of success are shown, for example, in European published patent application 0 363 019 A2 and German Gebrauchsmuster 91 03 574 U1 and 89 01 018 U1.
A further major problem arises that the surgeon before the intervention in the course of planning the operation with the help of surgical models, tries to shape the endoprosthesis optimally in advance, so that during the operation he is not further burdened with determining the optimal position of the spherical head on the base piece. Without additional means the surgeon on the following day, that is the day of the operation, stands in the operating room with the known joint endoprosthesis in exactly the same situation as during the operation planning, since no aids are available to him to again find the position of the ball joint on the base piece which was determined the day before to be optimal.
Given this background, it is the object of the present invention to further develop a spherical joint endoprosthesis of the above-described type, so that it enables the surgeon even during the surgery to make fine adjustments of the spherical head in relation to the base piece according to the individual needs of the patient, and further enables the surgeon to easily find during the operation (i.e., in situ) the optimal position of the spherical head on the base piece, which was previously determined during the planning of the operation.